Method for producing isocyanato-organosilanes

ABSTRACT

The invention relates to a method for producing isocyanato-organosilane of general formula (I) R 2 R 3 R 4 Si—R 1 —N═C═O. According to said method, gaseous carbamato-organosilane of general formula (II) R 2 R 3 R 4 Si—R 1 —NH—CO—OR (II), wherein R represents a monovatlent C 1 -C 10  alkyl radical, R 1  represents a bivalent C 1 -C 6  hydrocarbon radical and R 2 , R 3  and R 4  respectively represent a methyl, ethyl, n-propyl, i-propyl, methoxy, ethoxy, n-propoxy or i-propoxy radical, is heated in the presence of a heterogeneous catalyst.

[0001] The invention relates to a process for preparingisocyanatoorganosilanes and to certain isocyanatoorganosilanes.

[0002] For some time there has been great interest in an economic methodfor preparing isocyanatoorganosilanes in high yields and purities. Saidcompounds are of great economic importance, since they are used, forexample, industrially as adhesion promoters between organic polymers andinorganic materials (also termed coupling agents, crosslinkers).

[0003] For their preparation, processes are preferred in which startingmaterials are slightly or completely safe, in order to facilitatehandling and procedure. In the case of the processes previously used,isocyanatoorganosilanes are prepared in relatively low amounts inexpensive, low-efficiency processes.

[0004] For example, in the process described in U.S. Pat. No. 6,008,396,carbamatoorganosilanes are converted to the isocyanates in hot inertmedia with elimination of alcohol. However, this process. can only beoperated semi-continuously, since the concentration, of impurities inthe medium, even after a short time, increases in such a manner that thepurity of the desired product decreases significantly.

[0005] In the case of the process described in EP-A-1010704 forpreparing isocyanatoorganosilanes, carbamatoorganosilanes are thermallycleaved in the liquid phase to give the correspondingisocyanatoorganosilanes with catalysis by tin(II) chloride. Adisadvantage of this process is the highly complex process for isolatingand purifying the desired products, which leads to low yields.Therefore, this process has not been employed industrially to date.

[0006] The thermal cleavage of carbamatoorganosilanes in the gas phaseunder atmospheric or reduced pressure is disclosed by EP-A-649850.However, the yields are unsatisfactory.

[0007] The invention relates to a process for preparingisocyanatoorganosilane of the general formula 1

R²R³R⁴Si—R¹—N═C═O  (1)

[0008] in which gaseous carbamatoorganosilane of the general formula 2

R²R³R⁴Si—R¹—NH—CO—OR  (2)

[0009] where

[0010] R is a monovalent C₁-C₁₀-alkyl radical,

[0011] R¹ is a divalent C₁-C₆ hydrocarbon radical and

[0012] R², R³ and R⁴ are in each case a methyl, ethyl, n-propyl,isopropyl, methoxy, ethoxy, n-propoxy or isopropoxy radical,

[0013] is heated in the presence of a heterogeneous catalyst.

[0014] Using the inventive process, high yields and selectivities areachieved.

[0015] In the process, from the carbamatoorganosilanes of the generalformula 2, alcohols of the general formula ROH are eliminated, inparticular methanol, ethanol, propanol, butanol, isobutanol, pentanol,hexanol, isohexanol, cyclohexanol and 2-ethylhexanol. Preference isgiven to methanol and ethanol, particular preference to methanol.

[0016] The spacer R¹ between the organosilyl group and the carbamatogroup can be unbranched or branched saturated or unsaturated C₁-C₆hydrocarbon groups. Preference is given to alkyl radicals, in particularunbranched alkyl radicals, particular preference is given to methylene,ethylene and propylene.

[0017] R², R³ and R⁴ are preferably methyl, methoxy, ethoxy, n-propoxyor isopropoxy radicals.

[0018] Using the process, for the first time compounds of the generalformula 1 can be prepared where R², R³=methoxy, R⁴=methyl andR¹=methylene; R²=methoxy, R³=ethoxy, R⁴=methyl and R¹=methylene; R²,R³=ethoxy, R⁴=methoxy and R¹=methylene; or R², R³=methoxy, R⁴=ethoxy andR¹=methylene. These compounds are likewise subject-matter. of theinvention.

[0019] The heterogeneous catalysts are preferably selected fromcompounds of the groups consisting of Sn(I), Sn(II), Pb(II), Zn(II),Cu(I), Cu(II), Co(I), Co(II), Mg, Ca, Ba, Cr, Mo, Ti, V, W, Ce, Ni, P,Si, Al and mixed compounds and metals Pd, Pt, Co, Rh, Cu, Ag, Au, Zn,Cr, Mo, W, Cd and mixtures and alloys thereof. Catalytically activecompounds are, in particular, metal salts, for example acetates,oxalates, carbonates or sulfates. Preference is given to oxides ofmolybdenum, vanadium, tungsten and phosphorus, and also silicon oxidesor mixtures or mixed oxides of these, for example Ti₂O, Al₂O₃, BaO, CaO,MgO, CaO₂, Cr₂O₃, ZnO, V₂O₄, NiO, CuO, Co₃O₄, Fe(MoO₄) ₃. Furthermore,aluminosilicates, in particular zeolites, in varying pore sizes arepossible. Metal salts in the form of hydroxides, nitrates, tartrates,citrates, heteropolyacids and carbon modifications, for examplegraphite, transition metal nitrides and transition metal carbides canalso be used.

[0020] These metals, metal compounds or mixtures thereof are preferablyapplied to support materials, for example to glass wool, quartz wool,ceramics, oxidic compositions, such as SiO₂, Al₂O₃, steatite. Supportmaterials which can preferably be used are bodies in the form of spheres(customarily d=3-20 mm), rings (customarily d outer×h×d_(inner)=3-9mm×3-9 mm×1-7 mm), monoliths (those which are customary are, forexample, 1≈5-20 cm, d≈1-5 cm), cylinders (customarily d=3-20 mm),trilobes or pills.

[0021] The process is preferably carried out in a heated tubularreactor, in a coiled reactor or in a tube-bundle reactor. Customarymaterials, for example quartz glass or metals, can be used to producethese apparatuses.

[0022] The gaseous carbamatoorganosilane of the general formula 2 ispreferably catalytically converted in a temperature range of 150-1000°C., particularly preferably at the range 300-600° C., and in particularin a range of 400-500° C.

[0023] The process can be carried out with or without carrier gas, forexample nitrogen, or noble gases, such as argon.

[0024] The process is preferably carried out in a pressure range of0.01-100 bar, particularly preferably at 0.510 bar, in particular in arange of 0.5-1.5 bar.

[0025] The process can be carried out batchwise or, preferably,continuously.

[0026] As a result of the high product purity, the desired product canbe produced at high purity (>97%) in a simple distillation step. Theformation of six-membered isocyanurates, which has been observed at highthermal loads, is avoided by the present process.

1. A process for preparing isocyanatoorganosilanes of the generalformula 1 R²R³R⁴Si—R¹—N═C═O  (1) in which gaseous carbamatoorganosilaneof the general formula 2 R²R³R⁴Si—R¹—NH—CO—OR  (2) where R is amonovalent C₁-C₁₀-alkyl radical, R¹ is a divalent C₁-C₆ hydrocarbonradical and R², R³ and R⁴ are in each case a methyl, ethyl, n-propyl,isopropyl, methoxy, ethoxy, n-propoxy or isopropoxy radical, is heatedin the presence of. a heterogeneous catalyst.
 2. The process as claimedin claim 1, in which R¹ is methylene, ethylene or propylene.
 3. Theprocess as claimed in claim 1 or 2, in which R², R³ and R⁴ are methyl,methoxy or ethoxy radicals.
 4. The process as claimed in claims 1 to 3,in which the heterogeneous catalysts are selected from the groupcomprising compounds of Sn(I), Sn(II), Pb(II), Zn(II), Cu(I), Cu(II),Co(I), Co(II), Mg, Ca, Ba, Cr, Mo, Ti, V, W, Ce,. Ni, P, Si, Al andmixed compounds and metals Pd, Pt, Co, Rh, Cu, Ag, Au, Zn, Cr, Mo, W, Cdand mixtures and alloys thereof.
 5. The process as claimed in claims 1to 4, in which the reaction was carried out in a pyrolysis tube, in acoiled reactor or in a tube-bundle reactor.
 6. The process as claimed inclaims 1 to 5, which is carried out continuously.
 7. A compound of thegeneral formula 1 as claimed in claim 1, in which R², R³=methoxy,R⁴=methyl and R¹=methylene; R²=methoxy, R³=ethoxy, R⁴=methyl andR¹=methylene; R², R³ ethoxy, R⁴=methoxy and R¹=methylene; or R²,R³=methoxy, R⁴=ethyoxy and R¹=methylene.